Many people believe that when it comes to seafood, freshness is everything. But is that really the case? This article explores the complex relationship between freshness, flavor, and the way fish is processed and transported around the world.
The forms in which seafood is transported from fishing ports to consumption areas can be broadly divided into four categories: live fish, fresh fish, frozen fish, and processed products. We will omit the explanation of processed products, as it is self-explanatory. Regarding frozen fish, there are differences depending on the country. In the United States, fish that has been frozen and then thawed is also called “fresh fish.”In Japan, refrigerated fish or live fish that have been killed is called “fresh fish,” and when frozen fish is sold, it must be labeled as “thawed.”
In countries outside of Asia, “live fish” may refer to fish swimming in aquariums. Since it is not commonly seen in markets or supermarkets, we will explain it here.
Live fish, as the name suggests, refers to fish that are still alive, such as those kept in tanks or aquariums. They are transported from fishing ports in ships equipped with tanks or in specialized trucks with tanks on their cargo beds. There is also a dedicated section for live fish at the Toyosu Market. Once they are slaughtered, they become fresh fish.
One reason for the demand for live fish is that they can be caught from the tank while still swimming, prepared on the spot, and served. In addition to the freshness of the ingredients, there is also the value of the “experience” it offers customers, which can serve as an added value for restaurants. This applies to shrimp and squid “Odori.”
Another reason is that, depending on how they are processed after being caught, even the same individual fish can vary greatly in quality (amount of umami) and shelf life. For example, large fish that have been properlybled and had their nerves severed and fish that have died naturally after being caught (nojime) and have not been processed in any way (although they are cooled with ice) can have a shelf life difference of more than a week.The solution to this issue is live fish. Most seafood available in supermarkets in many countries is Nojime-processed.
Additionally, the state immediately after live fish are killeded is sometimes referred to as “seisengyo.” Depending on freshness, it is categorized as “seisengyo” (highly fresh) or “sengyo” (slightly less fresh). “Seisengyo” is used for raw dishes like sashimi or sushi, while ‘sengyo’ is primarily used for cooked dishes like grilled or simmered fish.
However, it is not that simple. Transporting and managing live fish involves various challenges, such as water quality deterioration, transportation costs, fish stress, and equipment investment.
In Japan, such extensive research has been conducted on freshness.
Of course, it’s a well-known fact among professional chefs that some fish don’t rely solely on freshness. Of course there is importance in freshness, but that’s just one element. It’s generally understood that flavor and taste improve with time (maturity).
The umami* found in the meat of the fish is essentially inosinic acid and glutamic acid. After a certain amount of time has passed after a fish has died, the body stiffens and not long after that the rigor lets up. The inosinic acid, which the umami is composed of, comes after the fish has stiffened. It then accumulates in the process of the body relaxing. This is the same in beef and pork in which there is no umami in the meat unless it is hung and matured for a time.
Therefore, ikizukuri sashimi that is still twitching usually won’t have the taste or depth of umami. However, the firm texture of sashimi is also an undeniable enjoyable aspect. It is not all about the umami.
*Glutamic acid, Inosinic acid and Guanylic acid are representative components of umami. Guanylic acid is found in kelp and vegetables (tomato, Chinese cabbage, green tea, etc.) as well as Parmesan cheese, inosinic acid is found in fish (bonito, macheral, sea bream, etc.) and meat (pork, chicken, etc.) while Guanylic acid is abundant in mushrooms (especially dried shiitake mushrooms).
We hope this information will be helpful.
Revision date: June 16, 2025
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